The Hobbit is often considered to be a lesser book when compared to JRR Tolkien's later opus, The Lord of the Rings. This is patent nonsense: the two novels are simply entirely different beasts, one a vivid but fuzzily drawn tale, the reading of which feels like a warm hearth and a mug of mulled wine, the other a thrilling yet terrifying vision of a world in which nightmarish creatures of genuine evil vie to destroy that kind of comfortable existence.

The disparity between the two books is also the reason why the casting of Martin Freeman in the central role of Bilbo Baggins – announced today – comes as such a relief. For Freeman is a quite different type of actor to Elijah Wood, who played Frodo as an overwrought, angsty, almost emo-ish little hobbit in Peter Jackson's film adaptations of the later tome.

If Frodo occasionally resembled a My Chemical Romance fan, Bilbo needs to be more like a minor official in a local branch of the Campaign for Real Ale. Getting the casting right is also absolutely vital because Baggins is one of the only a few fully rounded characters (Gandalf, Gollum and perhaps Thorin Oakenshield would be the others) in a story which, in line with its fairytale quality, is populated by creatures who are mainly sketched rather than drawn. Moreover, while Frodo is often a subject for other players to impose their hopes and fears onto, Bilbo is constantly at the heart of the action, carrying us with him. The other denizens of Middle Earth may be used to sly dragons, hideous goblins, giant spiders and mysterious elves, but Bilbo isn't, and neither are we. Just like us, he goes on a journey, and we see it unfold through his eyes. The actor who plays him needs to be able to embody this everyman quality perfectly, and I think in Freeman that Jackson has got his man.

At 39, the actor is the right age (Bilbo was older than Jackson's version of Frodo when he set out on his journey) and he certainly has that world-weary quality about him. One can just imagine him bumbling around his hobbit hole happily, perhaps planning a light mid-morning snack of a cake or two to follow a delicious breakfast, and being most disgruntled by the arrival of a company of dwarves and a wizard intent on enrolling him in a rather uncomfortable adventure. Bilbo is well-to-do and respectable, but crucially very ordinary (at least on the surface). And Freeman does quintessentially English ordinariness like no-one else in the business.

It's hard to read too much into the other casting decisions announced. If Jackson follows the tone of the book, characters such as Bombur, Fili, Kili, Oin and Gloin will barely register as individual personalities. Thorin Oakenshield, the leader of the dwarves, is a different matter. On screen he will need to be a more dynamic and charismatic character than he is in the book, a vital figure for whom one would gladly give one's life in battle. Jackson must have some confidence in Richard Armitage, best known from the BBC series Spooks, to have handed him the role.

Fortunately, the film-maker can rely on his Gandalf. The wizard will once again be played by the great Sir Ian McKellen, who so perfectly embodied the character's gruff warmth and kindly menace in the Lord of the Rings films. The news reports today do not mention Hugo Weaving, who made a passable Elrond in the earlier trilogy, even though the character appears in The Hobbit. A re-casting should not prove too much of a burden, since the half-human, half-elven figure is not a major player in the first book.

Speculation to that effect may have been given a slight boost when you look at some of the newly announced cast, which features a swath of actors well known from UK television: Armitage, and dwarves Aidan Turner (of BBC 3 drama Being Human), Robert Kazinsky (Sean Slater on Eastenders) and Graham McTavish (Lost) are all Brits, with the exception of Turner who is Irish. However, John Callen, Mark Hadlow and Peter Hambleton, who will play further members of the company, are Kiwis, and Stephen Hunter, who has been cast as rotund dwarf Bombur, is Australian. Currently, I'd say it looks like all bets are off.

• This article was amended on 25 October 2010. The original stated that Aidan Turner is British. This has been corrected.